Research On The Enhanced Heat Transfer Characteristics Of Spherically-convex Inner Finned Tubes

The development of various types of high-efficiency heat exchange equipment has become the main way to reduce energy consumption.In this paper,the spherical convex internal finned tube is studied on the basis of smooth internal finned tube.By changing the smooth inner finned tube structure to a raised shape to increase the heat transfer area.By changing the flow direction and resistance distribution of the fluid to enhance the disturbance of the fluid to the boundary layer,the heat transfer effect of the spherical convex inner finned tube is enhanced.In this paper,the heat transfer performance and flow resistance of spherically convex inner finned tubes are investigated using numerical simulation.The main conclusions are as follows.（1）A physical and mathematical model is established with a spherically convex inner finned tube as an example,and the accuracy of the simulation results is verified by comparing with the experimental data in the literature.Application of velocity vector,turbulent kinetic energy and velocity cloud diagram to analyze the enhanced heat transfer mechanism of three internal finned tubes.And compare the heat transfer performance and flow resistance of the three inner finned tubes,and get the largest heat transfer performance and flow resistance of the spherical convex inner finned tube.（2）The heat transfer performance and flow resistance of the spherical convex internal finned tube and the concave convex internal finned tube are compared,and it is concluded that the spherical convex internal finned tube has the best overall heat transfer performance index.Then the heat transfer performance and flow resistance of the spherical convex inner fin tube,conical inner fin tube and cylindrical inner fin tube are further compared.The results show that the spherical convex inner finned tube has the best heat transfer efficiency and the highest flow resistance.（3）Firstly,the heat transfer performance and flow resistance of different rows of spherical-convex inner fin tubes are compared.The results show that the nusser number Nu and the integrated heat transfer performance index f_tef increase with the increase of Re and the resistance coefficient decreases with the increase of Re for different rows of spherical convex inner finned tubes.The comprehensive heat transfer performance index of the two-row spherical convex internal finned tube is optimal.Next,comparing the heat transfer performance and flow resistance of different arrangements of ball and convex internal finned tubes,the resistance coefficient f of the wrong row of ball and convex internal finned tubes is obtained as the largest,and the comprehensive heat transfer performance index f_tefof the right row of ball and convex internal finned tubes is the largest.Then the heat transfer performance and flow resistance of the spherical convex inner fin tube with different numbers of fins were compared,and the integrated heat transfer performance index of the spherical convex inner fin tube with 8 fins was obtained to be the best.Finally,the enhanced heat transfer mechanism of the spherically convex inner finned tube with different fins was analyzed using velocity cloud,pressure cloud and temperature cloud diagrams.The results show that the heat transfer performance and the flow resistance of the spherically convex inner finned tube increase simultaneously with the increase of the number of fins.（4）Firstly,the main structural parameters of the spherically convex inner finned tube were analyzed using a single factor.The study shows that:the flow resistance and heat transfer performance of the ball-convex inner fin tube increase with the increase of the ball-convex radius r,the heat transfer performance and flow resistance increase with the thinning of the fin thickness t,and the ball-convex pitch p has little effect on the heat transfer characteristics and flow resistance.Then the multi-objective optimization of the spherically convex inner fin tube was carried out to analyze the effects of fin thickness t,spherically convex pitch p,and spherically convex radius r on the heat transfer performance and flow resistance of the spherically convex inner fin tube,and the optimal structural parameters were obtained as t=1.265 mm,p=14.31 mm,r=2.178 mm,and the objective functions Nu=79.21,f=0.01936,and f_tef=0.174.Finally,the sensitivity of the structural parameters of the spherically convex inner finned tube is analyzed.The results show that the heat transfer performance is mainly influenced by the fin thickness and ball convex radius,the resistance coefficient is mainly influenced by the ball convex radius,and the influence of fin thickness and ball convex radius on the comprehensive heat transfer performance index is relatively high.